An opportunistic radio communications system, for example a cellular opportunistic radio communications system, includes two types of equipment: terminals and radio communications network access units. A network access unit can serve a plurality of terminals in its coverage area.
These two types of equipment (terminals and network access units) use an opportunistic radio communications protocol.
In a cellular opportunistic radio communications system the opportunistic radio communications protocol defines various types of communications channel between a network access unit and the terminals that it serves. The opportunistic radio communications protocol also defines procedures for setting up and maintaining these communications channels.
Two types of communications channel are defined: pilot channels and traffic channels.
A pilot channel is a communications channel that supports signaling and exchanges relating to call control in opportunistic radio communications systems. A pilot channel is created by an access unit. A terminal is connected to an access unit via a pilot channel in order to set up a traffic channel to support a call. Each time the radio channel is lost or its quality is no longer able to meet its basic technical specifications, the terminal renegotiates the parameters of the traffic channel with the access unit via the pilot channel.
There are currently two approaches to defining a pilot channel in an opportunistic radio communications system.
With the first approach, the pilot channel is a dedicated physical channel. One or more bands of frequencies are reserved for supporting the pilot channel. It is not necessary for those frequency bands to belong to the set of frequency bands used for calls.
One drawback of that approach is that it requires static determination of frequency bands.
If the frequency bands dedicated to the pilot channel belong to the set of frequency bands used for calls, then that set must be sufficiently large for these frequency bands to meet traffic channel requirements as well as pilot channel requirements. Sizing is then based on the maximum number of traffic channels required, with the risk of those frequency bands being under used most of the time, leading to excessive consumption of frequency bands.
If the frequency bands dedicated to a pilot channel do not belong to the set of frequency bands used for calls, it is necessary to provide devices such as transmit/receive devices to enable these frequency bands to support a call.
Another drawback is that that approach implies a priori planning of the frequencies and identification of the frequency bands dedicated to supporting the pilot channel.
With the second approach, the pilot channel corresponds to an ultra wide band (UWB) physical channel. A UWB channel is then superposed on the spectrum of frequencies used for calls.
That approach has the drawback that for those frequency bands to be able to support a call it is necessary to provide procedures and devices such as transmit/receive devices.
There therefore exists a need for a technique for determining a pilot channel in an opportunistic radio communications system that does not require the use or provision of dedicated resources.